A SRM212 with one of those USB to barrell jack adapters and run it off a normal USB power bank.  4W should be just fine of a 2A output.   

Who is making these???

has to be one of the ones that can be set to 12v like this

Amazon.com: FARSENSE USB C to DC Adapter,Barrel PD Trigger Cable(3.3ft) with 10 Connector Tips,USB to DC Power Cable can Switch Voltage by Pressing The Key,Support LED Display Voltage : Electronics

Love it. How are you doing sir, still teaching? Any chance you'd take a glance at my McAllister mess/amp? I'd love to give it a refit. 

The thick film resistors are still bit of a problem cause of drift. Even with the dn2540, turning the trimmer a little too high or low will still cause it to drift.

9 minutes ago, psyduck said:

The thick film resistors are still bit of a problem cause of drift. Even with the dn2540, turning the trimmer a little too high or low will still cause it to drift.

then let's find some other kind resistors 😁

Just now, Michelag said:

then let's find some other kind resistors 😁

I think the metal film resistors will work, they're used on the cfaelectrostat board in google drive. It's quite a bit bigger and you need two of them for one channel.

52 minutes ago, psyduck said:

I think the metal film resistors will work, they're used on the cfaelectrostat board in google drive. It's quite a bit bigger and you need two of them for one channel.

guess i'm trying a mix MELF/thin film

10 hours ago, philodox said:

Love it. How are you doing sir, still teaching? Any chance you'd take a glance at my McAllister mess/amp? I'd love to give it a refit. 

i am retired now, 7+ years. And loving it.  Due to arthritis issues i am no longer working on any more equipment. including my own.  going to pay a couple of high-school kids to stuff and solder boards and chassis etc for new projects.

On 12/11/2025 at 1:27 AM, kevin gilmore said:

at the moment, do what i did 30 years ago.   srm212 plus 12v 7ah gel cell. its portable. kinda portable.

or buy 4 x apex opamps and run them class C with the dc to dc converters.

i wish i had a better solution. getting all those transistors to touch the heatsink at the same time is not easy.

even the koss box requires a decent size battery.  (6 x D cell) 

Well, there are true portable amplifiers, for example, the Stax D10, but its runtime is 3.5 hours. Which is pretty funny.

This HVRV can also be used with some kind of 12V power bank of a similar size.

But then we have to carry two boxes.

And why do we even need portable amplifiers..

Almost all Stax headphones are open-back.

Unless we using a Stax 4070.

But I think only a few people in the world have such a setup.
Probably no one does.
It's much more promising to simply have a portable, small amplifier that we can easily take  on a trip, for example, put in a suitcase.
The 10 kg kgsshv is hard to fit in a suitcase.
And this one is just right.

Edited December 13, 2025Dec 13 by Omega_ELS

9 hours ago, kevin gilmore said:

i am retired now, 7+ years. And loving it.  Due to arthritis issues i am no longer working on any more equipment. including my own.  going to pay a couple of high-school kids to stuff and solder boards and chassis etc for new projects.

Congrats! Enjoy retirement. Still a Legend. ❤️

being retired means i get to do what i want to do and when.

so the new thing based on the pioneer a09  (no not the a9) is also zero feedback, 120 watts into 8 ohms, damping factor of 100 and a thd about .001%.  the absolute perfect thing to drive your lundhal electrostatic transformers. 

basically the exactly same ubal/bal to bal board in the cfa3, and then the high power buffers.  pair of 30v 20 amp switching power supplies.

Nice... Side question, this any good?